Slip engaging portion of drill string formed of increased wall thickness and reduced hardness



March 5, 1963 c. F. HUNTSINGER 3,080,179

SLIP ENGAGING PORTION OF DRILL STRING FORMED I OF INCREASED VWALLTHICKNESS -AND REDUCED HARDNESS Fjiled Oct. 6, 195g: 5 Sheets-Shag: 1

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. IN VEN TOR. L192; II .H/A/TS/NGEE March 5, 1963 c. F. HUNTSINGER3,080,179

SLIP ENGAGING PORTION OF DRILL STRING FORMED OF INCREASED WALL THICKNESSAND REDUCED HARDNESS Filed Oct. 6, 1959 INVENTOR.

(be; EHU/VT-S/NGEE 14 77-0 A/EY.

March 5, 1963 v c. F. HUNTSINGER 3,080,172

' sup ENGAGING PORTION OF DRILL STRING FORMED v OF INCREASED WALLTHICKNESS AND REDUCED HARDNESS Filed Oct. 6, 1959 a Sheets-Sheet s 2! 55i 4 p40! a0 INVENTOR.

, I CARL E Hwvrswaee BY The present invention relates to rotary welldrilling equipment and more particularly to tubular drill string membersto be disposed in the well bore for rotating a drill bit, or the like,connected to its lower end. The tubular drill string may consist ofdrill pipe, light weight drill pipe, drill tubing, or drill casing. Forconvenience of reference, such tubular members may be classified asdrill pipe. This application is a continuation-in-part of my applicationfor Tubular Drill String Member for Drilling Well, Serial No. 810,035,filed April 30, 1959 and now abandoned.

The tubular drill string disposed in the well bore, to

the lower end of which the drill bit is attached, consists of aplurality of drill pipe members threadedly attached to one another. Thethreaded connections between the drill pipe sections are referred to astool joints, a male tool joint on one section being threadedly attachedto the female tool joint of an adjoining section.

During the operation of drilling the oil well, the drill bit eventuallybecomes dull or is to be changed for some other reason. Accordingly, theentire string of drill pipe is elevated in the well bore and the jointsof drill pipe disconnected from one another by unthreading the sectionsremoved from the hole from the sections that remain in the well bore.After the drill bit has been withdrawn from the Well bore, a new bit isattached to the lower end of the drilling string and the bit is insertedin the well bore, the tool joints being successively threadedly attachedto one another and the entire assembled drill string lowered in the wellbore until the new bit reaches the bottom of the hole, whereupondrilling is resumed. 'Normally, in drilling an oil well, a plurality ofdrill bits are used, requiring lowering and elevation of the entiredrill string in the well bore for a plurality of round trips.

During the making of a round trip, drill pipe sections above the-rotarytable at the top of the well bore are threaded or unthreaded from thedrill string disposed therebelow. The lower portion of the string ofdrill pipe is suspended or hung in the hole by a slip assembly thatusually consists of a plurality of segmentel slips having inner teethadapted to engage and grip the exterior of a pipe section and outerdownwardly tapering surfaces adapted to fit in a companion taperedsurface of a slip bowl. The weight of the string of drill pipe hangingin v the well bore tends to move the slips downwardly, wedging them inthe bowl and producing an inward force that causes the slip teeth'totend to penetrate into the drill pipe section that they engage. Withrelatively long strings of drill pipe in the well bore, the downwardforce is correspondingly greater, causing the radial pressure of theslips upon the pipe'section to be increased, and tending to elongate thepipe section where it is gripped by the slips, or collapse the sectioninwardly. The force imposed by the string of drill pipe itself isoftentimes greatly increased by the fact that it is very often caught bythe slip assembly during its lowering in the well bore, instead of beingbrought to a full rest prior to application of the slips therebyintroducing an impact load upon the slip assembly, caused by the jammingof the slips in the bowl and their inward pressure upon the pipe areawhich they grip.

During the unthreading and threading operations, in disice connecting orreconnecting each tool joint, tongs are used, which are placed upon theadjacent tool joints of the upper and lower sections. At times, thetongs gripping the lower section will slip or turn during the time thatthe upper tong is being used to either make or break the threadedconnection, eifecting a rotation of the lower string of drill pipe inthe slip assembly, causing the hard slip members to tend to mar or tearthe surface of the drill pipe that they engage. Such action can effect acutting and tearing of the pipe in the slip affected area.

During certain special threading or unthreading operation indisconnecting or reconnecting each tool joint, it is not practical toplace the tongs on the tool joints, but rather to place the tongsdirectly on the drill pipe. Also, certain types of drill pipe have notool joint connections but, rather, have the threaded connectionsdirectly on the drill pipe. Tongs also have sharp and hardened insertsto better grip the tool joints or drill pipe. The results of placing thetongs directly on the drill pipe will often effect a cutting, tearing ornotching action similar to that produced by the slip segment teeth whenapplied to the drill pipe. The gripping action applied by the tongs tothe drill pipe will often produce a localized crushing action. The abovetendency for the pipe section subjected to the gripping forces of theslips or tongs at the top of the well bore to be elongated or collapsedinwardly is more pronounced when lighter weight and higher strengthdrill pipe is used. Such use is dictated by increased hole depth, andalso by the desire to have a larger inside diameter through the stringof drill pipe to permit the pumping of greater volumes of drilling fiuidthrough the drill pipe to remove the cuttings at an increased rate andenhance penetration of the drill bit in the bottom of the well bore.

Lighter drill pipe weights enable less expensive surface equipment to beused inasmuch as such equipment does not have to support comparativelyheavy loads.

When comparatively light weight drill pipe is used, it is of a type thathad to be heat treated in order to increase its physical properties. Theparticular heat treatment employed results in a hardening of the steelof which the drill pipe is made, an increase inits strength, and adecrease in its ductility. The heat treatment also results in the steelbecoming more notch sensitive to cuts, tears or notches caused by slipor tong teeth than softer or lower strength steels. The notching of theexterior of a drill pipe section by the slips may be a source of fatiguefailure, and may ultimately result in. a twistoif or other disruption ofthe drill pipe at the location of the notch. The notching of acomparatively hard steel is potentially much more hazardous than that ofa soft steel since the notch or crack produced thereby advances muchmore rapidly, probably due to the fact that the metal does not yield toany appreciable extent to distribute the stress to which the pipe issubjected in the region of the notch.

It is evident that the relatively thin wall drill pipe is moresusceptible to inward crushing by the slips or tongs and to theprovision of cracks resulting from the notching of the outer portions ofthe drill pipe section subjected to the slip segment teeth, or to thetong segment teeth.

Accordingly, it is an object of the present invention to provide atubular drill pipe section of relatively light weight and thin wallthickness that is capable of better withstanding the inward crushingforce of the slips and tongs at the top of the well bore and which hasless notch sensitivity so as to be less conducive to fatigue failure.

Another object of the invention is to provide a drill pipe section of acomposite character and in which the main portion of the pipe section ismade of a material having-a relatively high unit strength, such mainportion having a 3. relatively thin wall thickness in comparison to itsoutside diameter. The drill pipe section at the area that will beengaged by the slips or tongs at the top of the well bore: is made of ametal that has a greater wall thickness in comparison to. itsdiameter soas to resist inward crushing by the slips or tongs, such metal alsohaving less notch sensitivity, so as to be less susceptible to fatiguefailure resulting from notches produced by the slips or tongs at the topof the well bore. A drill pipe section is thus producedv ofcomparatively light weight throughout its'over-all length, because ofits comparatively thin wall thickness, and which resists inward crushingof the slips or tongs and has less notch sensitivity. The metal havingthe greater wall. thickness and which is gripped by the slips or tongscan be of a lower grade than the main portion of the drill pipe section,but in view of its greater wall. thickness, it will be capable ofwithstanding the same loads as the main drill pipe section in tension,torsion, bending, and compression. This invention possesses many otheradvantages, and has other objects which may be made more clearlyapparent from a consideration of general forms in which it maybeembodied. These forms are shown in the drawings accompanying and formingpart of the present specification. They will now be described in detail,for the purpose of illustrating the general principles of the invention;but it is to be understood that such detailed description is not to betaken in a limiting sense, since thescopeofthe inventionis best definedby the appended claims.

Referring to the drawings:

FIGURE 1 is a side elevational view of a string of drillipipe embodyingthe invention;

FIG. 2 is alongitudinal'section through the upper portionof. a drill.pipe section, the lower portion beingshown in side elevation;

FIG. 3 is alongitudinal section through the lower portion ofadrill. pipesection, the upper portion thereof being shown in side elevation;

FIG. 4 isa side elevational viewv of a modification of thedrilllpipeshown in FIG. 1;

FIG; 5 is alongitudinal section, partly shown in side elevational,through the drill pipe section illustrated in FIG. 4;

FIG. 6. is. a longitudinal section, partly shown in side elevation,through another embodiment of a drill pipe section;

FIG.v 7 is a longitudinal section,. Partly shown in side l'evatiori,.of, a portion of still another drill pipe section;

FIG. 8 is a longitudinal section, partly in side elevation, of a portionof yet a further form of drill pipe section;

FIG. 9 is allongitudinal' section, with a portion illustr'atedv in sideelevation, of yet another embodiment of drill pipe section.

, As disclosed in FIGS. 1 to 3' of the drawings, a drillings'tringlOincludes a plurality of drill pipe sections 11, 12, 13 th'r'ad'edlyattached to one another. The upper end of each section may beconstituted asv a tool joint 14 having a threaded box 15 adapted to bethreadedly connected to the lower threaded pin 16 of a tool joint 17 atan adjacent upper drill pipesection. The. tool joints are suitablysecured to the intervening pipe 18 of each section in any'suitablemanner. As specifically. disclosed, the lower tool joint 17 is connectedto the adjacent portion. 18 of the pipe by a flash or pressure weld 19.The upper main portion of the drill pipe 18 is connected to a length. ofprotector tube 20, as by means of a flash or pressure weld 21, and theupper end of such protector tube section is, in turn, connected to theupper tool joint 14 by means of a flash or pressureweld 22. Although thedrawings specifically disclose the flash or pressure welds for securingthe several parts to one another, it is to 4 tool joint 17 may be madeintegral with the main length of drill pipe 18.

The main length of drill pipe 18 has a comparatively thin wall thicknessT in relation to its external diameter D for the purpose of providing alightweight pipe section 18 and to furnish an increased cross-sectionalpassage area P through which the drilling mud pumped down the drillingstring can flow, so as to minimize the frictional resistance to flow ofthe drilling mud through the string of drill pipe and insure itsdelivery at a greater volumetric rate through the drill bit (not shown).At the lower tool joint 17, the main section of drill pipe 18 has itswall thickness H increased by decreasing its internal diameter toconform to the internal diameter of the lower tool joint section 17.Similarly, the upper portion of the main drill pipe section has its wallthickness M increased by decreasing its internal diameter, such internaldiameter being essentially the same as the internal diameter through thelower tool joint 17. The upper tool joint 14 also has an internaldiameter substantially conforming to the internal diameter through thelower tool joint 17, and the intermediate section of protector tubing 20also preferably has an internal diameter substantially the same as theinternal diameter of the tool joints 14, 17 and an external diametersubstantially the same as the outside diameter of the main drill pipesection 18. The protector tube 20 is placed adjacent to the upper tooljoint 14, which is the region-of the drill pipe section normally engagedby the toothed slips 50 at the top of the well bore when disposed in aslip bowl 51 mounted in the usual rotary table 52. Such protector tubeis of such a length as to insure that the entire length of the slipteeth will engage such section, and not the main drill pipe section 18therebelow. For example, the protector tube portion 20 of the drill pipemember may be about fortytwo inches in length; whereas the entire drillpipe section 14, 20, 18, 17 may be about thirty feet in length.

The main portion 18 of the drill pipe section is made of a relativelyhigh strength steel that has been heat treated. Such steel has acomparatively high ultimate tensile strength, a comparatively high yieldstrength, and a relatively low elongation; Its hardness is alsorelatively high- As an example, the portions of the drill pipe. section.just referred to may be grade P- drill tubing. having the followingphysical characteristics:

Despite its highv strength, such steels, or steels similar toit, havehigh notch sensitivity, and in view of the fact that the wall thicknessT of the pipe section. is comparatively small, such steels aresusceptible to inward crushing by the slipsat the top. of the Well home.However, the protector tube section 20 has an ultimate tensile strengthand yield strength that is substantially lower than that of the mainportion .18 of the drill pipe section, while its elongation issubstantially higher. I-ts hardness is also substantially lower. By wayof example, the protector tubular section 2-0 that is to be engaged bythe slips at the top of the well bore may be made from grade B tubing,which has the following physical characteristics:

Ultimate tensile strength .p.s.i 118,800 Yield' strength p.s.i 84,400

.material between the upper tool joint 14 the weight per foot over onlya Elongation percent 23.0 Rockwell hardness No. (1-22-25.

and the following chemical analysis:

Percent Carbon 0.37 Manganese 0.93 Silicon 0.16 Molybdenum 0.03

The grade B drill pipe 20 has a much greater wall thickness than theunderlying portion of the tubular member, and since its outside diameterD to Wall thickness M is much less than the corresponding outsidediameter D to wall thickness T of the main section of the tubularmember, it is capable of withstanding inward crushing to a much greaterextent than the main portion 13 of the tubular member. Since it is alsonot as hard as the main portion of the tubing section, it has lessernotch sensitivity, and despite the penetration of the slips, or othertoothed members, such as tong segments, into its surface, fatiguefailures do not result.

Despite the fact that the unit strength of the protector tube 20 issomewhat less than that of the main portion 18 of the drill pipesection, it is capable of withstanding at least the same tensile loads,compressive loads, bending loads and torques. This is due to the fiactthat its crossssectional area is greater than the cross-sectional areaof the main portion 18 of the drill pipe section. Its greater wallthickness, which is provided by having substantially the same outsidediameter as the main portion 18 of the drill pipe section, and an insidediameter that is no less than the inside diameter through the adjacenttool joint 14, results in a considerable increase in its resistance toinward crushing by the slips.

By way of example, the drill pipe, with the exception of the protectortube portion 20, may be made of grade P-l05 steel. The main portion 18of the drill pipe section may be of 3 /2 inches 0.1)., and have a Weightof 9.2 lbs. per foot. Assuming that the grade P-l05 pipe has aguaranteed minimum yield strength of 105,000 p.s.i., and that theprotector tube portion 20 is made of grade E pipe having a guaranteedminimum yield strength of 75,- 000 p.s-.i., the protector tube portionwill have the same tensible strength as the main portion of the drillpipe-if the weight per foot of the protector tube is 9.2105,000+7s,e00=12.9 lbs. per foot Typically, the protector tube 20 withthe grade E material that is used can have a weight of 13.3 lbs. perfoot. By inserting such a Weight of grade B and the main portion 18 ofthe drill pipe section, the protector tube 20 will have a tensilestrength at least equal to that of the main portion of the drill pipesection. In the examples given, a grade P-105 pipe section has a yieldstrength in crushing of approximately 7,000 lbs., while the protectortube has a yield strength in crushing of approximately 26,000 lbs.Accordingly, the crushing yield 1 strength of the protector tube 20 isalmost four times that the drill pipe string, while short length ofabout three to four feet has been increased by less than fifty percent.This has been done without restricting the passage through the section241 of drill pipe below that of the inside diameter through the usualtool joints 14, 17.

It is, accordingly, apparent that :a drill pipe section has beenprovided in which a heavier cross-sectional area of pipe 2%) is presentat the region of engagement with the slips at the top of the well bore,which will better resist of the main portion 18 of localized crushingunder the action of the slip segments.

Despite the fact that the protector tube section has a lesser unittensile strength than the main portion 18 of the drill pipe section, theelongation due to excessive tensile loads will be no greater because ofthe much heavier cross-sectional area of the protector tube. The

material of which the protector tube is made has a much lower notchsensitivity than the main portion 18 of the drill pipe section, and,therefore, offers less opportunity for fatigue cracks to develop, withpotential resultant fatigue failure at the region of engagement of thepipe by the slips. If the protector tube 20 becomes excessively marredby the slip teeth, it can easily be cut out and a new section insertedin its place, thereby avoiding the necessity for scrapping the entirelength of drill pipe.

Although the protector tube disclosed in FIGS. 1, 2 and 3 has beendescribed in connection with the application of slips to the protectortube section 20, it is also applicable to the engagement of suchprotector tube portion by tongs having sharp and hardened inserts. Theteeth of such tongs can have the same harmful effect-on the .drill pipesection as described above specifically in connection with engagement ofslips with a drill pipe section. Moreover, the protector tube portion 24can be applied between the lower tool joint 17 and the main portion 18of the drill pipe section as well as between the upper tool joint 14 andthe drill pipe section 18 as shown in FIGS. 4 and 5. When locatedbetween the lower tool joint 17 and the main drill pipe section 18, theprotector tube section 2.0 will ordinarily be engaged by tongs havingthe sharp and hardened inserts. Such lower protector tube portion willbetter Withstand the cutting, tearing, not-ching and localized crushingaction of the tong segments than the main portion 18 of the drill pipesection, which is of high strength and has greater susceptibility tonotching andlocalized crushing.

In the form of invention disclosed in FIG. 6, a drill pipe section 12has a flush internal diameter throughout its length, that is to say, theinternal diameter through the tool joints 14, 17 and protector tubes213a the same as the internal diameter through the main portion 18a ofthe pipe section. The main portion or length 18a of the pipe section hasits wall thickness M increased at each of its upper and lower parts byincreasing its external diameter, and this external diameter willconform to the external diameter of each protector tube 211a, which hasthe greater Wall thickness M than the lesser Wall thickness T of themain section 1&1 of the drill pipe. As in the forms of inventionpreviously described, the main portion 18a is connected to eachprotector tube 20a, as by means of a flash or pressure weld 21. The endof each protector tube remote from the main portion 18a can also beconnected to its adjacent tool joint 14, 17 in any suitable manner, asby means of a flash or pressure weld 22.

Again, in lieu of the flash or pressure weld, the several parts can bethreadedly attached to one another.

In all respects, the drill pipe section disclosed in'FIG. 6 is the sameas that illustrated in FIGS. 2 and 5, in that each protector tube Zi ais made of a material having a lesser unit strength than the mainportion 18a of the drill pipe section, which is compensated for by thefact that its wall thickness is much greater. In this instance, thegreater wall thickness is secured by increasing the outside diameter ofthe protector tube 212a rather than decreasing the inside diameter, asillustrated in FIGS. 2 and 5. Thus, inward crushing action of slips ortong segments is resisted. The fact that the protector tube portion 20::is not as hard as the main portion 18a of the V for attachment to theadjacent tool joint.

drill pipe section renders it less susceptible to notching, minimizing,if not fully eliminating, fatigue failures.

In the form of invention disclosed in FIG. 7, the main portion 18b ofthe drill pipe section 12 may be Welded or otherwise secured to an uppertool joint 14 or a lower tool joint 17, or to both upper and lower tooljoints 14, 17, the ends of the main portion being thickened to provide alarger wall thickness M and cross-sectional area Each thickened area, inefiect, provides a shoulder 36 against which a tube 2% abuts that isplaced over the main portion 15b of the drill pipe section and along aparticular length of such section, which may be three to four feet, forexample. A tube 2% can be first heated and then slipped over the mainportion of the drill pipe section until it engages the shoulder 30. Uponcooling, the tube 20b shrinks upon the pipe section and is thus firmlysecured thereto. If desired, the tube 20b can be slipped over the drillpipe section 18b and then welded thereto at its upper and lower ends, asindicated at 21, 22.

The tube 2012 adds to the thickness of the drill pipe at the region ofengagement by the slips of the rotary table or by the toothed tongsegments, and thereby provides a composite drill pipe section which isbetter able to withstand the inward crushing action of the slips ortongs. Moreover, the tube 2% may be made of a steel having essentiallythe same physical characteristics as the steel described above fromwhich the protector tube sections 20 and 20a are made, which steel isnot as hard as the steel of which the main tubing section 18b is made,and which will, therefore, have a lesser notch sensitivity so thatfatigue failures do not result, regardless of the penetration of theslip or tong segment teeth thereinto.

In the form of invention disclosed in FIG. 8, the protector tube 20c isdisclosed as being integral with the adjacent tool joint 14, 17, and isattached to the main portion or length 18a of the drill pipe section 12With an internal flush fluid passage through the tool joint, protectortubes and main tubing section. The drill pipe section is essentially thesame as disclosed in FIG. 6, with the exception that each tool joint isintegral with the adjacent protector tube portion 20c. In other words,each tool joint and adjacent protector tube portion 200 are made fromthe same steel, have much lesser notch sensitivity than the steel of themain section 18a and are better capable of withstanding inward crushing.Accordingly, it is only necessary to provide a separate welded orthreaded connection 21 between the end of the protector tube portionremote from the tool joint and the adjacent end of the main portion 18aof the drill pipe section.

In the form of invention disclosed in FIG. 9, the protector tube portion20d having the greater wall thickness is integral with the main portionor length 180 of the drill pipe section and is made from a steel havingthe same chemical analysis. Each protector tube portion 20d is made of asuitable length, such as three to four feet, and has a greater wallthickness M than the thickness T of the main portion of the section. Itis welded, or otherwise secured, to the adjacent tool joint 14, 17.However, the heat treatment of the main portion 180 of the tubularmember or drill pipe section is diiferent from the heatv treatment ofthe protector portion 20d in order to provide the proper characteristicsto these different portions. As an example, the entire drill pipesection 12 can be heat treated to provide the appropriate physicalcharacteristics desired in the thin wall portion T of the section,including high ultimate tensile strength, high yield strength,relatively low elongation and relatively high hardness. Each protectortube portion 20d is then made softer so that it is less notch sensitiveby simply tempering the length of the protector tube 20d in a subsequenttempering operation without reheating the main thin wall portion 18c ofthe pipe section.

Another manner of securing the desired physical characteristics inthemain portion 180 of the drill pipe section 12 and in the protectortube portion 20d is to normalize the full length of the drill pipe 12and then air quench the entire pipe section 12. Since each protectortube portion 20d is heavier than the thin wall main portion 180 of thepipe section, the cooling rate of each protector tube portion isappreciably'slower than the main portion, with a resultant lower unitstrength and hardness in the thicker wall protector tube portions 20d.

The device illustrated in FIG. 9 can be made in several manners prior toits heat treatment. It can be hot rolled to the desired outside diameterof the protector tube portions 20d and the desired wall thickness. It

can then be cold drawn through a split die on a draw bench to achievethe reduced wall thickness T of the main portion of the pipe. Theconstant internal diameter through the main portion 1-8c and each protector tube portion 20d can be maintained with a punch; whereas the splitdie accomplishes the change in outside diameter from the lesser diameterof the main length 180 of the drill pipe section to the greater diameterof the protector tube portions 20d.

The inventor claims:

1. A tubular drill pipe section to be used in a well bore comprisingupper and lower tool joints, a main steel tubular portion extendingupwardly from said lower joint and terminating near said upper tooljoint, and an elongate steel protector tube extending downwardly fromsaid upper tool joint and secured to the upper end of said main portion,said main portion having a much lesser wall thickness throughoutsubstantially its entire length than said protector tube and being madeof a steel having substantially greater hardness and unit tensile andtorsional strength than the steel of said protector tube, the length ofsaid protector tube being about at least four times the outside diameterof said main portion and said protector tube being disposed in saiddrill pipe section at a location for engagement by supporting slips atthe top of the well bore, the cross-sectional area of said protectortube being such that the total tensile and torsional strength of saidprotector tube is no less than the total tensile and torsion-a1 strengthof said main portion, whereby said protector tube has less notchsensitivity and greater resistance to inward crushing than said mainportion to the action of the slips.

2. A tubular drill pipe section to be used in a well bore comprisingupper and lower tool joints, a main steel tubular portion extendingupwardly from said lower joint and terminating near said upper tooljoint, and an elongate steel protector tube extending downwardly fromsaid upper tool joint and secured to the upper end or said main portion,said main portion having a much lesser wall thickness throughoutsubstantially its entire length than said protector tube, the wallthickness of said main portion adjacent said protector tube beingsubstantially the sameas the wall thickness of said protector tube, saidmain portion being made of a steel having substantially greater hardnessand unit tensile and torsional strength than the steel of said protectortube, the length of said protector tube being about at least four timesthe outside diameter of said main portion and said protector tube beingdisposed in said drill pipe section at a location =for engagement bysupporting slips at the top of the well bore, the cross sectional areaof said protector tube being such that the total tensile and torsionalstrength of said protector tube is no less than the total tensile andtorsional strength of said main portion where it has the aforesaidlesser wall thickness, whereby said protector tube has less notchsensitivity and greater resistance to inward crushing than said mainportion to the action of the slips.

3. A tubular drill pipe section to be used in a well bore comprisingupper and lower tool joints, a main steel tubular portion extendingupwardly from said lower joint and terminating near said upper tooljoint, and an elongate steel protector tube extending downwardly fromsaid upper tool joint and secured to the upper end of said main portion,said main portion having a much lesser wall thickness throughoutsubstantially its entire length than said protector tube and being madeof a steel having substantially greater hardness and unit tensile andtorsional strength than the steel of said protector tube, the length ofsaid protector tube being about at least four times the outside diameterof said main portion and said protector tube being disposed in saiddrill pipe section at a location for engagement by supporting slips atthe top of the well bore, the cross-sectional area of said protectortube being such that the total tensile and torsional strength of saidprotector tube is no less than the total tensile and torsional strengthof said main portion, the inside'diameter of said protector tube beingno less than the inside diameter of said upper tool joint, where by saidprotector tube has less notch sensitivity and greater resistance toinward crushing than said main portion to the action of the slips.

4. A tubular drill pipe section to be used in a well bore comprisingupper and lower tool joints, 2. main steel tubular portion extendingupwardly from said lower joint and terminating near said upper tooljoint, and an elongate steel protector tube extending downwardly fromsaid upper tool joint and secured to the upper end of said main portion,said main portion having a much lesser wall thickness throughoutsubstantially its entire length than said protector tube, the wallthickness of said main portion adjacent said protector tube beingsubstantially the same as the wall thickness of said protector tube,said main portion being made of a steel having substantially greaterhardness and unit tensile and torsional streng-th than the steel of saidprotector tube, the length of said protector tube being about at leastfour times the outside diameter of said main portion and said protectortube being disposed in said drill pipe section at a location forengagement by supporting slips at the top of the well bore thecross-sectional area of said protector tube being such that the totaltensile and torsional strength of said protector tube is no less thanthe total tensile and torsional strength of said main portion where ithas the aforesaid lesser wall thickness, the inside diameter of saidprotector tube being no less than the inside diameter of said upper tooljoint and the inside diameter of said main portion adjacent saidprotector tube, whereby said protector tube has less notch sensitivityand greater resistance to inward crushing than said main portion to theaction of the slips.

5. A tubular drill pipe section to be used in a well bore and adapted tobe engaged by gripping slip segments or tong segments used in supportingand threadedly attaching or unthreading drill pipe sections to or fromone another, comprising upper and lower tool joints, a main steeltubular portion between said joints, and an elongate steel tubularprotector portion between and secured to said main portion and one ofsaid joints and adapted to be engaged by gripping segments, said mainportion having a much lesser wall thickness throughout substantially itsentire length than said protector portion, the steel of said mainportion having different physical characteristics than the steel of atleast the outer portion of said protector portion, such that said mainportion has substantially greater hardness and unit tensile andtorsional strength than the steel of said outer portion, the length or"said protector portion being about at least four times the outsidediameter of said main portion, the cross-sectional area of saidprotector portion being such that the total tensile and torsionalstrength of said protector portion is no less than the total tensilestrength of said main portion, whereby the outer portion of said tubularprotector portion has less notch sensitivity than said main portion tothe action of the gripping segments and said tubular protector portionhas greater resistance to inward crushing than said main portion to theaction of the gripping segments.

6. A tubular drill pipe section to be used in a well bore and adapted tobe engaged by gripping slip segments or tong segments used in supportingand threadedly attaching or unthreading drill pipe sections to or fromone another, comprising upper and lower tool joints, a main steeltubular portion between said joints, and an elongate steel tubularprotector portion between and secured to said main portion and one ofsaid joints and adapted to be engaged by the gripping segment, said mainportion having a much lesser wall thickness throughout substantially itsentire length than said protector portion, the steel of said mainportion having different physical characteristics than the steel of saidprotector portion, such that said main portion has substantially greaterhardness and unit tensile and torsional strength than the steel of saidrotector portion, the length of said protector portion being about atleast four times the outside diameter of said main portion, thecross-sectional area of said protector portion being such that the totaltensile and torsional strength of said protector portion is no less thanthe total tensile and torsional strength of said main portion, wherebysaid tubular protector portion has less notch sensitivity and greaterresistance to inward crushing than said main portion to the action ofthe gripping segments.

7. A tubular drill pipe section to be used in a well bore and adapted tobe engaged by gripping slip segments or tong segments used in supportingand threadedly attaching or unthreading drill pipe sections to or fromone another, comprising upper and lower tool joints, a main steeltubular portion between said joints, and an elongate steel tubularprotector portion integral with said main portion and secured to one ofsaid joints and adapted to be engaged by the gripping segments, saidmain portion having a much lesser wall thickness throughoutsubstantially its entire length than said protector portion, said mainportion and protector portion being composed of steel having the samechemical analysis, but having different physical characteristics, suchthat said main portion has substantially greater hardness and unittensile and torsional strength than the steel of said protector portion,the length of said protector portion being about at least four times theoutside diameter of said main portion, the cross-sectional area of saidprotector portion being such that the total tensile and torsionalstrength of said protector portion is no less than the total tensile andtorsional strength of said main portion, whereby said tubular protectorportion has less notch sensitivity and greater resistance to inwardcrushing than said main portion to the action of the gripping segments.

8. A tubular drill pipe section to be used in a well bore and adapted tobe engaged by gripping slip segments or tong segments used in supportingand threadedly attaching or unt-hreading drill pipe sections to or fromone another, comprising upper and lower tool joints, a main steeltubular portion between said joints, and an elongate steel tubularprotector portion between said main portion and one of said joints andadapted to be engaged by the gripping segments, said protector portionhaving an inner portion integral with said main portion and secured tosaid one joint and also having an outer portion encompassing said innerportion, said main portion having a much lesser wall thicknessthroughout substantially its entire length than said protector portion,the steel of said main portion having different physical characteristicsthan the steel of said outer portion, such that said main portion hassubstantially greater hardness and unit tensile and torsional strengththan the steel of said outer portion, the length of said protectorportion being about at least four times the outside diameter of saidmain portion, the cross-sectional area of said protector portion beingsuch that the total tensile and torsional strength of said protectorportion is no less than the total tensile and torsional strength of saidmain portion, whereby the outer portion of said tubular protectorportion has less notch sensitivity than said main portion to the actionof the gripping segments and said tubular protector portion has greaterresistance to inward crushing than said main portion to the action ofthe gripping segments.

9. A tubular drill pipe section to be used in a well bore and adapted tobe engaged by gripping slip segments or tong segments used in supportingand threadedly attaching or unthreading drill pipe sections to or fromone another, comprising upper and lower tool joints, a main steeltubular portion between said joints, and upper and lower elongate steelprotector portions between and secured to said main portion and saidjoints, each of said protector portions being adapted for engagement bythe gripping segments, said main portion having a much lesser wallthickness throughout substantially its entire length than each of saidprotector portions, the steel of said "main portion having difierentphysical characteristics than the steel of at least the outer portion ofeach of said protector portions, such that said main portion hassubstantially greater hardness and unit tensile and torsional strengththan the steel of the outer portion of each of said protector portions,each of said protector portions having a length about at least fourtimes the outside diameter of said main portion, the cross-sectionalarea of each of said protector portions being such that the totaltensile and torsional strength of each of said protector portions is noless than the total tensile and torsional strength of said main.portion, whereby the outer portion of each of said tubular protectorportions has less notch sensitivity than said-main portion to the actionof the gripping segments and each of said tubular protector portions hasgreater resistance to inward crushing than said main portion to theaction of the gripping segments.

References Cited in the file of this patent UNITED STATES PATENTS1,236,145 Burns Aug. 7, 1917 1,613,461 Johnson Jan. 4, 1927 1,714,813Reed May 28, 1929 1,973,848 Duffy Sept. 18, 1934 1,993,269 Fletcher M31.5, 193 5 2,257,335 Evans et a1 Sept. 30, 1941 2,340,706 SOmeS Feb. 1,1944 FOREIGN PATENTS 129,918 Australia June 18, 1946 849,532 Ger-manySept; 15, 1952 865,883 German F65. 5; 1953

1. A TUBULAR DRILL PIPE SECTION TO BE USED IN A WELL BORE COMPRISINGUPPER AND LOWER TOOL JOINTS, A MAIN STEEL TUBULAR PORTION EXTENDINGUPWARDLY FROM SAID LOWER JOINT AND TERMINATING NEAR SAID UPPER TOOLJOINT, AND AN ELONGATE STEEL PROTECTOR TUBE EXTENDING DOWNWARDLY FROMSAID UPPER TOOL JOINT AND SECURED TO THE UPPER END OF SAID MAIN PORTION,SAID MAIN PORTION HAVING A MUCH LESSER WALL THICKNESS THROUGHOUTSUBSTANTIALLY ITS ENTIRE LENGTH THAN SAID PROTECTOR TUBE AND BEING MADEOF A STEEL HAVING SUBSTANTIALLY GREATER HARDNESS AND UNIT TENSILE ANDTORSIONAL STRENGTH THAN THE STEEL OF SAID PROTECTOR TUBE, THE LENGTH OFSAID PROTECTOR TUBE BEING ABOUT AT LEAST FOUR TIMES THE OUTSIDE DIAMETEROF SAID MAIN PORTION AND SAID PROTECTOR TUBE BEING DISPOSED IN SAIDDRILL PIPE SECTION AT A LOCATION FOR ENGAGEMENT BY SUPPORTING SLIPS ATTHE TOP OF THE WELL BORE, THE CROSS-SECTIONAL AREA OF SAID PROTECTORTUBE BEING SUCH THAT THE TOTAL TENSILE AND TORSIONAL STRENGTH OF SAIDPROTECTOR TUBE IS NO LESS THAN THE TOTAL TENSILE AND TORSIONAL STRENGTHOF SAID MAIN PORTION, WHEREBY SAID PROTECTOR TUBE HAS LESS NOTCHSENSITIVITY AND GREATER RESISTANCE TO INWARD CRUSHING THAN SAID MAINPORTION TO THE ACTION OF THE SLIPS.